The gamma Dor variable HR 8799: results from a multisite campaign

In this paper, we present the results of a multisite photometric campaign devoted to the gamma Doradus type variable HR 8799. From Johnson and Stromgren data, we were able to identify three independent frequencies (f(i) = 1.9791 cycle d(-1), f(2) = 1.7268 cycle d(-10) and f(3) = 1.6498 cycle d(-1)) as well as another signal, which we are able to identify as the coupling term between two of the frequencies (f(4) = f(1) - f(2) = 0.2479 cycle d(-1)). These four frequencies are able to account for all of the observed variations down to the la significance level. We discuss another possible interpretation of these frequencies using a model of quasi-stochastic amplitude modulation. In this scenario, we are able to show that HR 8799 might be pulsating with two independent frequencies, one of which undergoes amplitude modulation similar to other gamma Dor objects. In addition, we discuss a preliminary mode identification based on the observed colour curves. Finally, 18 simultaneous, high-resolution echelle spectra were collected on two nights and we qualitatively compare the radial velocities from these data with our photometry.